Apparatus and method for heating and melting solid lubricants in the delivery drum

ABSTRACT

An apparatus for heating and melting solid lubricants in a delivery drum, including a heating element composed of armored resistors shaped as concentric rings and junction spokes. A hoist lowers and raises the heating element into and out of the drum via vertical rods that are not heated. A first thermal sensor is connected with the heating element, and a second thermal sensor is mounted on the vertical rods. A transfer pump withdraws melted lubricant from the drum via a suction tube having a bottom valve at its foot. A lubricant delivery tube is connected to the output side of the pump.

The present invention relates to an apparatus and related method forheating and melting solid lubricants (Hot-Melts) in the delivery drum,to allow their transfer by pumping into the containers for servicingoiling machines, specifically electrostatic ones.

Solid lubricants for laminates, known also as “Hot Melts”, “Dry-film”,“Dry-lube”, etc. are solid products at room temperature and theirmelting point is in the order of 30+50° C.

They are usually delivered in metal drums capable of being fully opened,into which they were poured by the manufacturer.

For their use in electrostatic oiling machines, they must be liquefiedby heating beyond the melting point.

This can be obtained in various known manners, for instance usingelectric shell drum heaters, or introducing the drums themselves intoheated chambers and leaving them therein until the content is fullymelted.

It is then necessary to move the warm drums and transfer their contentinto the thermostatic service containers of the oiling machines.

However, this operation is not only impractical, it also requires verylong times and a great expenditure of energy.

This is due to the fact the heat conductivity of the solid mass of thelubricant is very poor and therefore the energy applied to the exteriorof the container (shell heaters, hot chambers) penetrates very slowlyinto the mass.

The product near the walls of the drum melts rather rapidly, but thetemperature within the solid mass rises at an extremely slow rate,because of the poor heat conductivity of the product and of the absenceof convective currents.

The present invention aims to reduce the time required for melting andfacilitate transferring the product.

According to the present invention, heating bodies are set down on theupper surface of the solid mass and—progressively sinking into it—theybring thermal energy directly into the core of the mass itself.

As the product melts around the heating bodies, it is animated byconvective motions which in turn effectively transmit heat to theadjacent solid mass with progressive expansion of the exchange surface.The liquefaction process thus extends at a growing rate to the entiremass contained in the drum.

When melting is completed, a pump, having its body heated, draws theproduct from the drum and sends it—through a pipeline, which is alsoheated—to the service container of the oiling machine.

The apparatus according to the invention described hereafter withreference to FIGS. 1 and 2 is an effective practical embodiment of theseprinciples.

A heating element constituted by armoured resistors shaped as concentricrings and junction spokes 1 borne by a hoist 2 is set down onto theupper surface of the product 3 to be melted contained in the originaldrum of the product 4. The heating element is subjected to the thrustderiving from its own weight and that of the connected movable masses(rod of the hoisting cylinder, load-bearing arms, transfer pump, suctiontube, etc.).

At this point the heating element is powered, controlling itstemperature by means of a heat sensor 5 applied thereto, at a value T1sufficient for melting but such as to avoid a harmful local overheatingof the product.

Note that the vertical rods 6 that connect the heating elements to theload-bearing arm are not heated: since they remain outside the productfor a long time, if they were heated they would rapidly reach very highsurface temperatures, such as to damage the product when they enteredit.

Under the effect of the heating and of gravity, the heating elementstarts to sink into the mass that progressively melts around it. Theliquefied product—agitated by convective currents—carries the heat andin turn transfers it to the surrounding solid surfaces with amultiplying effect.

When the heating element reaches the bottom dead centre of its traveland is near the bottom of the drum, the entire mass is liquefied withthe exception of a few residual nuclei.

The heating element is therefore kept at the temperature T1 for anadditional time, in order to allow the entire mass to melt. At thispoint, temperature control passes to a second sensor 7 mounted on thevertical rods at about one third of their length starting from thebottom, which regulates the maintenance temperature T2. The value T2 isselected slightly above the melting temperature of the product. Theproduct can remain at this temperature T2 even for long times withoutundergoing any alteration of any kind.

When all the product is liquid, the transfer pump 8 can be startedmanually or as a result of a command originating from the automationsystem.

The tube for the delivery of the product 10 is heated for example bycirculation of a diathermic fluid within a jacket positioned coaxially.

By way of example, the pump can be started when the signal that theproduct is totally liquefied and the signal of minimum level in therelated service container are both present simultaneously.

The pump is stopped after a time corresponding to the transfer of theentire capacity of the drum. A bottom valve 9 mounted at the foot of thesuction tube 11 prevents it from emptying, facilitating the priming ofthe pump in subsequent operations.

When the drum is empty, the hoist is raised to the top dead centre (seeFIG. 1 b) with a manual command. The empty drum can thus be replacedwith a full one and the entire operation can be repeated for a number oftimes n.

Melting times depend on the heat capacity and on the melting point ofthe product to be treated, as well as—obviously—on ambient temperature.

By way of example, with ambient temperature 15° C. and melting point ofthe product of 45° C., the entire content of the drum is melted in about5 hours with a power of 3 kW and a temperature of the heating element of90° C.

At equal ambient temperature, using a conventional electrical drumheater (shell plus bottom) having a power of 5.5 kW and workingtemperature of 120° C., the time for the complete melting of a drum ofHot-Melt is about 18 hours. Similar times are required by heatedchambers. Aside from any energy and economics-related considerations,this length of time is unacceptable.

An oiling machine applying 1 g/m² of Hot-Melt on the two surfaces of a1500 mm wide metal strip at an average speed of 150 m/min. consumes:

2×1.5 mm×1 g/m²×150 m/min=450 g/min−0.5 l/min. Therefore, a 200 litredrum is consumed in 400 min, i.e. in less than 7 hours.

Hence, a single-drum heating and melting station would not assure thecontinuous operation of the line.

The present invention instead assures the continuous operation in mostpractical cases, with very modest energy requirements.

LIST OF REFERENCES

-   1 heating element-   2 hoist-   3 upper surface of the product-   4 drum of the product-   5 thermal sensor-   6 vertical rods-   7 maintenance sensor-   8 transfer pump-   9 bottom valve-   10 pre-heated delivery tube-   11 suction tube

1-6. (canceled)
 7. An apparatus for heating and melting solid lubricantsin a delivery drum, comprising: a heating element composed of armoredresistors shaped as concentric rings and junction spokes; a hoistadapted to lower and raise said heating element into and out of saiddrum; vertical rods that connect said heating element to components ofsaid hoist, wherein said vertical rods are adapted to be unheated; afirst thermal sensor operatively connected with said heating element; asecond thermal sensor mounted on said vertical rods; a transfer pump forwithdrawing melted lubricant from said drum via a suction tube; a bottomvalve mounted at a foot of said suction tube; and a lubricant deliverytube connected to an output side of said pump.
 8. An apparatus accordingto claim 7, wherein said heating element is subjected to thrust derivedfrom its own weight and the weight of movable masses of said verticalrods, components of said hoist, said transfer pump, and said suctiontube.
 9. An apparatus according to claim 7, wherein said delivery tubeis coaxially disposed in a jacket, and wherein a diathermic fluid isadapted to circulate within said jacket for heating said delivery tube.10. A method of operating the apparatus of claim 7, including the stepof controlling the temperature of said heating element by means of saidfirst and second thermal sensors at a melting temperature and amaintenance temperature respectively, wherein said temperatures arepredetermined for melting said lubricants but are such as to preventharmful overheating thereof.
 11. A method according to claim 10, whereinafter said heating element has reached a bottom dead center of said drumupon at least substantial melting of the entire mass of said lubricant,said first thermal sensor keeps said heating element at said meltingtemperature until the entire mass of said lubricant is melted.
 12. Amethod according to claim 11, wherein said second thermal sensor ismounted on said vertical rods at approximately one third of their heightas measured from a bottom thereof, and wherein after the entire mass ofsaid lubricant has been melted, said second sensor keeps said heatingelement at said maintenance temperature.